Showing papers on "Ecosystem published in 1982"

Soil carbon pools and world life zones

Abstract: Soil organic carbon in active exchange with the atmosphere constitutes approximately two-thirds of the carbon in terrestrial ecosystems1,2. The relatively large size and long residence time of this pool (of the order of 1,200 yr) make it a potentially important sink for carbon released to the atmosphere by fossil fuel combustion; however, in many cases, human disturbance has caused a decrease in soil carbon storage3,4. Various recent estimates place the global total of soil carbon between 700 (ref. 2) and 2,946 × 1015 g (ref. 5) with several intermediate estimates: 1,080 (ref. 1), 1,392 (ref. 6), 1,456 (ref. 3), and 2,070 × 1015g (ref. 7). Schlesinger's3 estimate seems to be based on the most extensive data base (∼200 observations, some of which are mean values derived from large studies in particular areas) and is widely cited in carbon cycle studies. In addition to estimating the world soil carbon pool, it is important to establish the relationships between the geographical distribution of soil carbon and climate, vegetation, human development and other factors as a basis for assessing the influence of changes in any of these factors on the global carbon cycle. Our analysis of 2,700 soil profiles, organized on a climate basis using the Holdridge life-zone classification system8, indicates relationships between soil carbon density and climate, a major soil forming factor. Soil carbon density generally increases with increasing precipitation, and there is an increase in soil carbon with decreasing temperature for any particular level of precipitation. When the potential evapotranspiration equals annual precipitation, soil carbon density9 is ∼10 kg m−2, exceptions to this being warm temperate and subtropical soils. Based on recent estimates of the areal extent of major ecosystem complexes9,10 which correspond well with climatic life zones, the global soil organic carbon pool is estimated to be ∼1,395 × 1015g.

Nutrient cycling and nutrient use efficiency

Abstract: Forest ecosystems systematically produce more litterfall dry mass per unit of nitrogen in sites with less aboveground nitrogen circulation. This pattern is observed both within and among tropical, temperate deciduous, coniferous, Mediterranean, and fertilized ecosystems. The differences among sites are probably related to differences in soil nitrogen availability. Patterns of nitrogen use for root and wood production probably reinforce the litterfall results. An examination of phosphorus and calcium use efficiency for litterfall production yields more ambiguous results. The pattern for nitrogen circulation and nitrogen use efficiency in forests has important implications for ecosystem-level properties, including the development of low nitrogen availability in soil.

Temporal succession in a desert stream ecosystem following flash flooding

Abstract: Recovery of a desert stream after an intense flash flooding event is described as a model of temporal succession in lotic ecosystems. A late summer flood in Sycamore Creek, Arizona, virtually eliminated algae and reduced invertebrate standing crop by 98%. Physical and morphometric conditions typical of the preflood period were restored in 2 d and the biota recovered in 2—3 wk. Algal communities responded rapidly and achieved a standing crop of nearly 100 g/m2 in 2 wk. Community composition was dominated by diatoms early in succession and by filamentous greens and blue—greens later. Macroinvertebrates also recolonized denuded substrates rapidly, largely by immigration of aerial adults and subsequent oviposition. Growth and development were rapid and several generations of the dominant mayfly and dipteran taxa were completed during the 1st mo of recovery. Invertebrate dry biomass reached 7.3 g/m2 in 1 mo. Gross primary production (Pg) measured as O2 increased in a similar asymptotic fashion and reached 6.6 g°m—2°d—1 in 30 d. Pg exceeded community respiration (R) after day 5 and Pg/R averaged 1.46 for the remainder of the 2—mo sequence. This ecosystem is thus autotrophic and exports organic matter downstream and by drying, laterally. Uptake of nitrate and phosphorus were proportional to net primary production and exhibited a marked downstream decline in concentration during both light and dark periods. Temporal trajectories of various community and ecosystem attributes are compared with those suggested by Odum (1969) to be diagnostic of successional status. Agreement was poor in attributes which are especially modified in open, frequently disturbed ecosystems such as streams.

Aspects of the Stability and Resilience of Savanna Ecosystems

Abstract: Savannas are among the most variable of terrestrial ecosystems. They undergo large and frequent changes in production, composition and structure and they contain some of the worst examples of degradation by man. There are, accordingly, many references to them as “fragile” and “brittle” ecosystems, with frequent predictions of imminent “collapse”. But these terms have been used loosely, as jargon, and we need now to progress beyond this vague terminology. What, precisely, do we mean by these terms? Is it possible to be more precise? More specifically, can we achieve an understanding of the equilibrium behaviour of savannas? For this deals with how they change, and how much they can change before the change is irrevocable.

Arctic tundra: A source or sink for atmospheric carbon dioxide in a changing environment?

Abstract: Intact cores from the wet coastal arctic tundra at Barrow, Alaska, were used as microcosms in the measurement of CO2 fluxes between peat, vegetation, and atmosphere under controlled conditions. Net ecosystem CO2 uptake was almost twice as high at present summer temperatures (4° C) than at 8°. Lowering the water table from the soil surface to -5 cm also had a pronounced effect in decreasing net ecosystem carbon storage. Warming of the tundra climate could change this ecosystem from a sink for atmospheric CO2 to a source.

Fire and Nutrient Cycling in Temperate Ecosystems

Abstract: Wildfire is an integral component of many temperate ecosystems. The impact of wildfire on the nutrient dynamics of an ecosystem is dependent on the proportion of biomass and nutrients aboveground, which is therefore susceptible to combustion. Mechanisms for postfire nutrient conservation are most strongly developed in nutrient-poor (oligotrophic) ecosystems, in which most of the nutrients are found aboveground, and least well developed in nutrient-rich (eutrophic) ecosystems, whose nutrients are predominantly belowground. (Accepted for publication 21 October 1981)

Organic carbon spiralling in stream ecosystems

Abstract: stream, we show that S is closely related to Fisher and Likens' ecosystem efficiency. Unlike efficiency, however, S is independent of the length of the study reach, and values of S determined in streams of differing lengths can be compared. Using data from three different streams, we found the relationship between S and efficiency to agree closely with the model prediction. Hypotheses of stream functioning are discussed in the context of organic carbon spiralling theory.

Ecosystem Analysis of the Tallgrass Prairie: Nitrogen Cycle

Abstract: Nitrogen cycling in tallgrass prairie was studied by using nitrogen content and concentration data for various ecosystem components on grazed and ungrazed tallgrass prairie in northeast Oklahoma. The seasonal dynamics of N in various plant parts was described, and the annual flow of N among different compartments was calculated. A simulation model was used to study the effect of grazing, fertilization, irrigation, and fire on nitrogen cycling. The results show that grazing, fertilization, and irrigation increase the nitrogen cycling rates. Annual spring fires reduce plant uptake and mineralization of N from plant parts, while mineralization of N from organic matter is increased.

The nutrient balance of an amazonian rain forest

Abstract: Nutrient balance studies of mature ecosystems have shown that in many cases leaching losses are greater than atmospheric inputs. If the systems are not degrading, this means that the net losses must be compensated for by weathering of parent material. In contrast to ecosystems with rates of nutrient leaching that are higher than rates of atmospheric input, leaching of nutrients from an Amazonian rain forest ecosystem was less than or equal to input from the atmosphere every year between 1975 and 1980. If this forest is not aggrading this means that weathering of parent materials does not play an important role in the nutrient economy of the ecosystem. The forest apparently maintains itself on nutrients derived from the atmosphere.

Material transfer in a western Oregon forested watershed

Abstract: Abiotic transfer of organic and inorganic materials by a diverse family of processes is an essential part of all natural, large-scale ecosystems. Physical processes of material transfer are particularly important in the coniferous forest biome, which contains many geologically youthful and geomorphically active landscapes. High-relief, steep hillslope and channel gradients, dense vegetation, massive trees, and heavy precipitation result in a complex relationship among material transfer processes and vegetation. In a strict sense, material transfer involves erosion, transport, and deposition. This is equivalent to current usage of the term "sedimentation," which geologists and engineers use to describe transfer of predominantly inorganic material. In a system with significant depositional sites, material transfer includes routing of material through a variety of storage compartments. In this study, which deals mainly with a small, steep watershed where storage opportunities are limited, we emphasize annual material transfer rates and roles of vegetation but do not attempt to quantify deposition and storage. Material transfer has several important roles in the functioning of foreststream ecosystems. It is an important mechanism for nutrient redistribution and particularly nutrient export from ecosystems. Erosion and deposition create landforms that offer contrasting habitat opportunities for terrestrial and aquatic organisms on a variety of temporal and spatial scales. Erosion may also determine rates and patterns of succession following or during either erosion disturbances (for example, landslide) or disturbance of vegetation alone (for example, wildfire or insect infestation). These effects may be localized to the scales of root-throw mounds and landslide scars (generally <2000 m2) or they may extend over broad areas covering many hectares. There is also a variety of ways in which vegetation regulates rates of erosion processes. These influences of vegetation may result in reduced erosion by the effects of ground cover and rooting strength, or in increased erosion, as in the case of trees serving as a medium for transfer of wind stress to the soil mantle.

Pesticides and Ecosystems

Abstract: More than 500,000 tons of pesticides are produced annually for application in US agroecosystems to control insect pests, plant pathogens, and weeds (USDA 1980). As little as 1% of this may actually hit the target organisms (PSAC 1965). Instead, most reaches nontarget sectors of agroecosystems and/or spreads to surrounding ecosystems as chemical pollutants. Most investigations of pesticide effects on the environment have focused either on populations of nontarget species or on the degree of contamination of land, water, and air (Pimentel 1971, Edwards 1973a,b, Brown 1978). Few investigations or reviews have centered on the effects of pesticides on whole ecosystems. In particular, relatively little information exists on most aspects of the effects of pesticides on whole ecosystems including species diversity, ecosystem stability, food chains, energy flow, nutrient cycling, genetics of organisms, and physical resources. To identify aspects of the structure and dynamic interactions within ecosystems susceptible to stress by pesticides, we have summarized available information on the range of specific changes in ecosystems that may take place when they are exposed to pesticides and have assessed current knowledge on potential effects of pesticide stresses on ecosystems.

Desert Ecosystems: Their Resources in Space and Time

Abstract: The dynamics of desert ecosystems control levels of resources that are essential to the survival of desert biotas. Because precipitation is both low and relatively unpredictable in arid regions, the climates, topographies, and soils, of these areas present formidable constraints to resource availability in space and time. And for the same reason, the processes of production, consumption, decomposition, and nutrient-cycling in deserts are also highly irregular and difficult to predict with accuracy. For example, global models relating actual evapotranspiration to primary production and decomposition apply poorly in arid regions.Surprisingly great amounts of carbon are stored in desert soils, particularly in caliche deposits which represent a major ‘sink’ of carbon from the atmosphere. In Arizona desert soils, inorganic carbon exceeds organic carbon by a factor of > 10. Direct use of organic carbon is made principally by organisms that break down desert litter and simultaneously cause relatively high rates of nitrogen mineralization. While nitrogen is traditionally considered deficient in arid environments, its flux is considerable because of high rates of gain by fixation and loss by denitrification and volatilization. Nitrogen accumulates in ‘islands of fertility’ beneath desert shrubs where it becomes relatively available because of (i) its high concentration in plant litter, and (ii) reduced activity of any aromatic modifiers that retard decomposition.It is misleading in deserts to relate nutrient availability to yearly averages, as nutrients may become highly available following pulses of ‘effective’ precipitation. Moreover, mineralization and subsequent availability to plants of phosphorous, the ‘master element’ in nutrient cycling, are moderately independent of nitrogen mineralization and can proceed rapidly. Clearly, the case for nutrient deficiency in deserts may be overstated.Consumption of primary production has varying effects on rates of resource availability in desert ecosystems. Generally weak regulation of primary production is predicted for consumers of green vegetation, except occasionally during early drought. Carnivores should exert variable controls over their prey, while pollinators, seed-eaters, and detritivores—most of which are strongly soil-associated—should have the greatest impacts on primary production and nutrient cycling.

N2-fixing cyanobacteria: Why they do not become dominant in shallow hypertrophic lakes

Abstract: Species shifts and succession phenomena in lakes of increasing trophic state were considered in detail, using the basic information on the growth kinetics of the species involved. Successively we dealt with the succession from green algae to cyanobacteria in eutrophic lakes and the competitive interactions between N2-fixing and non-N2-fixing cyanobacteria in eutrophic-hypertrophic lakes. The competing species could be placed along an irradiance gradient; their position being defined by their light-energy requirements. Further, when a N2-fixing organism was involved, the competitive interaction could be defined under different sets of irradiance values and nitrate concentrations. The growth kinetic data, obtained under laboratory conditions, provided the basic information to explain why hypertrophic lakes are less favourable to N2-fixers, even when a N-limitation prevails. The trophic state of the lake is of major importance and is decisive with regard to which species will dominate.

Competition for nitrogen in a tussock tundra ecosystem

Abstract: The objective was to measure the competition for nitrogen among vascular plants, mosses, and soil microbes along a continuum of nitrogen availability, induced by carbon and nitrogen amendments, in a tussock tundra ecosystem.15N was used as a tracer. Vascular plants showed an increasing15N recovery with increasing time and with increasing nitrogen availability; the latter suggests that nitrogen was limiting vascular plant growth. Green mosses took up15N initially, but showed no significant trends with either treatment or time. There was a higher15N recovery in the soil insoluble compartment for the carbon-amended treatment than in the nitrogen-amended treatments; this suggested that carbon as an energy source limited microbial activity. After two months, the relative15N recovery fell in the order: soil microbes (≈79%)>vascular plants (≈16%) >green mosses (≈2%).

Leaf area, light transmission, roots and leaf damage in nine tropical plant communities

Abstract: The vertical distribution of leaf area by species; transmission of photosynthetically active radiation; root biomass and fine-root surface area; and leaf damage were measured in nine tropical ecosystems: six in Costa Rica and three in Mexico. Ecosystems studied included monocultures of maize (young and mature) and sweet potato; year-old natural succession and vegetation designed to mimic succession; a 2.5-year-old mixture of three arborescent perennials (cacao, plantain, Cordia alliodora); 2.7-year-old plantation of Gmelina arborea; coffee shaded by Erythrina poeppigiana; and an old, diverse wooded garden. Leaf area index ranged from 1.0 in young maize to 5.1 in natural succession and the gmelina plantation. The vertical distribution of leaves was most uniform in diverse ecosystems, and most clumped in species-poor ecosystems. Light transmission was inversely proportional to leaf area, and two dense-canopied monocultures (sweet potato and gmelina) were nearly as effective at light capture as were some of the more diverse ecosystems. Optical density of the canopy ranged from 2.0 ( Large roots (> 5 mm diameter) accounted for most root biomass in the older ecosystems at a soil dept of 5–25 cm, and fine roots ( 2.0 m2 m−2 of ground. Total root surface area increased with age and diversity, and the monocultures — even those effective at light capture — had low root surface area. Herbivore damage on leaves of 35 species ranged from 16% of leaf area. Heavily damaged species contributed less to total ecosystem leaf area than did species damaged less than average. Ecosystem-level damage was not well correlated with age or diversity. Leaf damage in all ecosystems ranged from about 2 to 10% of leaf area, or 25 g m−2 of ecosystem. Young monocultures do not necessarily capture less light, provide less soil cover, and experience more herbivory than older, more diverse ecosystems. However, root surface area (and therefore possible nutrient-capture ability) is high only in ecosystems that are diverse or old, and this is an important design consideration for agroecosystems appropriate for the humid tropical lowlands.

Nutrient cycling in forests of the Pacific Northwest

Abstract: Ecosystem analysis has established nutrient cycling as an important area of ecology involving biological, chemical, and geological interactions. Studying the flow of elements through ecosystems provides us with a tool for understanding the functioning of ecosystems. For example, if an ecosystem component has a rapid flux of elements through it, or if it stores large amounts of an element, that component is clearly important in ecosystem function. Nutrient cycling strongly influences ecosystem productivity since nutrient flows are closely linked with transfers of carbon and water. In addition nutrient cycling may also affect succession and evolution in forest ecosystems. Various distinct processes are involved in nutrient cycling, such as decomposition, weathering, uptake, leaching, and so on. Each is a precursor to another and the flow of nutrients follows a set of interconnected steps. Although the basic nutrient cycling processes are common to all ecosystems, the rates of the processes vary from one forest ecosystem to another. This variation plays an important role in forest succession and evolution. For example, long-term foliage retention by conifers may allow a species to exist where only a marginal nutrient supply is available from the soil. Nitrogen-fixing species, on the other hand, can occupy sites where nitrogen availability is low because they can provide their own nitrogen. An understanding of nutrient cycling is thus essential for the rational management of forest ecosystems. Nitrogen is recognized as the most limiting element for forest growth in the Pacific Northwest, particularly in Douglas-fir (Pseudotsuga menziesii) ecosystems (Gessel and Walker 1956; Gessel et al. 1969). For this reason this chapter focuses largely on nitrogen cycling. Cycling of other elements such as potassium and calcium are compared with that of nitrogen, where contrasting behavior may provide insight into nutrient-cycling processes. The objectives of this chapter are to (1) briefly describe the important nutrient cycling processes; (2) contrast nutrient cycles in different forest eco-

Water chemistry profiles in an early- and a mid-successional forest in coastal British Columbia

Abstract: Water chemistry profiles of an 18-year-old forest ecosystem are compared with those of a 70- to 90-year-old forest ecosystem for a 9-month period. The younger ecosystem was dominated by Douglas-fir...

Comparison of the Feeding Behaviour of Calanus and Pseudocalanus in two Experimentally Manipulated Enclosed Ecosystems

Abstract: INTRODUCTIONImplicit in some recent models of the dynamics of planktonic systems, for example that of Steele & Frost (1977) is the concept that filter-feeding copepods may be scaled by size when considering feeding in relation to the size composition of their paniculate food. For a particular organism ingestion of phytoplankton has been considered to be a function of its own weight and the size composition of the phytoplankton available to it. Such scaling has been assumed to occur both in an intra- and interspecific sense, with model development involving a ‘large’ copepod {Calanus) able to feed and grow more efficiently on ‘large’ cells (diatoms) and a ‘small’ copepod {Pseudocalanus) better adapted to feed on ‘small’ cells (flagellates). However, although the general relationship between growth and metabolic rate and body size is widely accepted (Banse, 1976; Fenchel, 1974) this relationship between dietary particle-size composition and size of organism has remained a working hypothesis with little experimental support..

Transport of Particulate Organic Carbon Through the North Inlet Ecosystem

Abstract: Tidal fluctuations and transports of particulate organlc carbon (POC) were investigated at 3 marsh creeks (near Georgetown, South Carolina, USA) comprising the major transfer points between the North Inlet Marsh and the adjoining aquatic ecosystems. Two creeks, Town and North Jones, form the inlet mouth and are the only marsh-ocean exchange points. The third creek, South Jones, connects to a brackish water embayment. The creeks were simultaneously sampled every 1.5 h for 50 consecutive hours during neap tides (4 tldal cycles) and 50 consecutive hours during corresponding spring tides of each season. At the inlet. POC concentrations fluctuated in-phase with the tide during the winter and out-of-phase with the tide during the summer Combinations of in-phase and out-of-phase patterns occurred in spring and fall. The fluctuations at the brackish water location were irregular POC concentrations were similar in each season with values averaging about 1.4 g mP3. Net transports varied from tidal cycle to tidal cycle with regard to direction of transport (import or export) and magnitude, ranging from a net import of 240 g POC S-' to a net export of 228 g POC S-'. Annual budgets revealed Town Creek to export POC at a rate of 2.6 ? 0.5 X log g yr-'; North Jones Creek imported POC at a rate of 3.8 ? 0.7 X 10a g yr-l; and South Jones Creek exported POC at a rate of 5.5 k 0.8 X 108 g yr-' The 3222 ha North Inlet marsh serves as a source of POC to the ocean at a rate of 87 2 16 g of POC per m2 yr-l.

Nitrogen cycling in United Kingdom forests: the relevance of basic ecological research

Abstract: Following recent reviews on nutrient cycling in temperate and British forests, two aspects of N cycling are selected for examination because of their fundamental importance and their relevance to management-ecosystem research and mobilization of N during decomposition. Despite the early work by J. D. Ovington and P. J. Rennie, only two major forest ecosystem studies have been developed in Britain. Summaries from these ecosystems show that they span the range of temperate forests in the N cycling characteristics. The Pinus nigra plantation on Culbin Sands is functioning on a low capital with low rates of transfer and shows N deficiency after 40 years. In contrast, the mixed deciduous Meathop Wood has a much larger capital of N and higher rates of transfer. The Pinus ecosystem retained a high proportion of added fertilizer N in the biomass and forest floor, and increased growth rates can be explained through N recycling within the trees. Basic concepts of N mineralization are reviewed and it is shown that they need to be modified for application to forests. Uptake by saprophytic and mycorrhizal fungi from the pool of soluble organic N can short-circuit the ammonification pathway and N can be released from substrates with a high C:N ratio by lysis of microbial tissues and faunal feeding. Some examples of evidence of these processes are given, stressing the spatial and temporal mosaic of substrates acting as sinks and sources of N. Management practices can have a marked effect, not only on the quantity of N returned in residues, but on its availability as a result of variation in the associated carbon. However, growth experiments have shown that substrates with C:N ratios above 35 can release significant amounts of N to tree seedlings. A final examination of the recycling processes in the four nutritional stages of a forest emphasizes the importance of the effects of management on the short- and long-term balance of mobilization processes in the forest soil.

Recent increase in mercury sedimentation in a forest lake attributable to peatland drainage

Abstract: In order to gain information about the natural background levels and about the recent history of mercury in Finnish waters, mercury profiles were determined in two lakes in which annually laminated sediment is deposited, and which differ from each other with respect to the history of land use in their drainage areas. Annual sediment laminations or varves allow a precise dating of the studied sequence, and their existence indicates undisturbed recording of the history of the environment.

Decomposers and the fire cycle in a phryganic (East Mediterranean) ecosystem.

Abstract: Dehydrogenase activity, cellulose decomposition, nitrification, and CO2 release were measured for 2 years to estimate the effects of a wildfire over a phryganic ecosystem. In decomposers' subsystem we found that fire mainly affected the nitrification process during the whole period, and soil respiration for the second post-fire year, when compared with the control site. Our data suggest that after 3-4 months the activity of microbial decomposers is almost the same at the two sites, suggesting that fire is not a catastrophic event, but a simple perturbation common to Mediterranean-type ecosystems.

Carbon, phosphorus and nitrogen budgets of the littoral Equisetum belt in an oligotrophic lake

Abstract: Stores and flows of carbon, phosphorus and nitrogen in a littoral Equisetum stand were studied in 1978–1980 in the oligotrophic, mesohumic lake Paajarvi, southern Finland. The major carbon and nutrient stores were sediment and Equisetum. The seasonal cycle of the macrophyte vegetation had a profound influence on the whole littoral ecosystem. In spring, when only dead remains of Equisetum were present above ground, there were few differences in nutrient, chlorophyll a and zooplankton concentrations between the littoral and the open lake; phytoplankton and epiphytes were the major producers.